The lowdown on the Millers new signing...
After starting his career in non-league Derbyshire signed for Blackburn Rovers and made his professional breakthrough after a successful loan spell with Wrexham.
He became a regular for Blackburn during the 2006/2007 campaign where he opened his senior account for the club with a goal in a 3-0 victory over Wigan Athletic. He finished the season with nine goals in all competitions. In the same season he received a call-up to the England under-21 squad making his international bow in a 3-3 draw with Italy in a game where he also scored.
The following season he was heavily involved in Blackburn’s Premier League campaign and netted on the opening day of the season in a 2-1 victory over Middlesbrough.
His performances became noticed at home and abroad resulting in an initial loan switch to Greek giants Olympiacos in 2009 where his impressive goals tally ensured a permanent move at the end of the 2008/2009 season for a fee believed to be £3million.
He bagged a brace in the Greek Cup final after a 3-3 draw with AEK Athens before Olympiacos came through on a penalty shootout.
After a loan spell with Birmingham City in 2010 he signed for Nottingham Forest on a permanent basis in 2011, he has also enjoyed loan spells with Oldham Athletic and Blackpool.